feat(ai): read the importer's deck and transcript cache; studio DraftWriter fits DraftSink as is

Retrieval now reads <dataDir>/cache/decks/<courseId>/<deckId>/text.json and
<dataDir>/cache/transcripts/<courseId>/<lessonId>.json (skipped when the lesson
has a transcript file). DraftSink returns { location?, branch?, commit? }, so
the studio's createDraftWriter(ctx) needs no adapter; generateDraft computes
paths itself and reports the draft branch.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/feature-ai/src/web/GeneratePage.tsx

@@ -5,7 +5,7 @@ import { Field, PageHead } from "./components";
 
 interface CourseOpt { id: string; title: string }
 interface Sources { lessons: { id: string; title: string; type: string; module: string; hasText: boolean }[]; files: string[]; cache: string[] }
-interface Job { id: string; status: "queued" | "running" | "done" | "failed"; progress: number; message: string | null; error: string | null; result: { location: string; paths: string[]; warnings: string[] } | null }
+interface Job { id: string; status: "queued" | "running" | "done" | "failed"; progress: number; message: string | null; error: string | null; result: { location: string; branch?: string; commit?: string; paths: string[]; warnings: string[] } | null }
 
 const KINDS = [
   { value: "document", label: "Document" },
@@ -178,7 +178,7 @@ export default function GeneratePage() {
           {job.status === "failed" ? <p className="ai-error">{job.error}</p> : null}
           {job.result ? (
             <>
-              <span className="ai-hint">Saved as a draft at <span className="ai-mono">{job.result.location}</span>. Review it in the studio before publishing.</span>
+              <span className="ai-hint">{job.result.branch ? "Committed to your draft branch " : "Saved as a draft at "}<span className="ai-mono">{job.result.location}</span>. Review it in the studio before publishing.</span>
               <ul className="ai-rows">{job.result.paths.map((p) => <li key={p}><span className="ai-path">{p}</span><span className="ai-meta">draft</span></li>)}</ul>
               {job.result.warnings.length ? (
                 <div className="ai-section">